1. Field of the Invention
This invention relates to a process and apparatus for delivering supercritical fluid and in particular to a process and apparatus that utilizes a high pressure vessel to deliver supercritical fluid.
2. Description of the Prior Art
Previously, supercritical fluid has been delivered through the use of high pressure pumps such as syringe pumps, membrane pumps and dual-piston pumps. Due to the high pressure requirements, these pumps are extremely expensive and are often prone to leaking, thereby reducing the efficiency. Also, these pumps can be unreliable for the delivery of fluids whose critical temperatures are below or slightly above room temperature. Since the supercritical fluid has a much lower viscosity than a "normal" liquid, the pump "leaks" if its head is above the critical temperature of the fluid. To solve this problem, it is necessary to cool off the heads, thereby increasing the complexity of the process. Further, the membrane and dual-piston pumps deliver fluid in pulses. In addition, all of the pumps are noisy. While syringe pumps can develop a high pressure quickly and do not produce a pulsating output, they have a small volume which may necessitate refilling the pump partway through an extraction process with which the pump is being used. Also, syringe pumps are more expensive than other pumps. In addition, the greater the pressure that a pump must produce, the greater the difficulty in controlling leakage and, generally, pumps are not used to produce a pressure greater than 10,000 psi. Pumps are subject to long term maintenance.